1. Field of the Invention
The present invention relates to a Josephson logic circuit. Especially, it relates to a logic circuit which is effective for forming an OR circuit, an AND circuit, or a majority logic circuit.
2. Description of the Prior Art
To rapidly process information, an electronic apparatus such as an electronic computer should operate rapidly and should be small in size.
Therefore, a Josephson element which has a much higher operation speed than does a conventional semi-conductor integrated circuit element should be considered for use as a functional element of an electric computer.
A logic circuit which utilizes such a Josephson element as a functional element, is current injection type of logic circuit. An AND circuit of current injection type in a logic circuit has a high input current margin. However, a function which separates the input and the output is not provided, and therefore, the AND circuit must be combined with an OR circuit.
A circuit which utilizes an asymmetrical Superconducting Quantum Interference Device (SQUID) element is also proposed to be employed in the AND circuit. However, in such an AND circuit, due to the threshold characteristics of the SQUID, the input signal level is dependent on the bias current level, with the result that the margin of operation is small.
Further, in an AND circuit which utilizes a Josephson element, a large amount of current is required to operate the AND circuit. Therefore, the whole output of the logic gate, that is, for example, an OR circuit connected to the previous stage of the AND circuit, should be injected into the AND circuit. Consequently, the number of outputs of the logic gate is limited to one.
If the AND circuit can be operated on a small output of the OR circuit connected to a next stage of the circuit, then a plurality of logic circuits or logic gates can be operated on the full output of the OR circuit.